1. Field of the Invention
This invention relates to the recovery of metal values, e.g., gallium, from aqueous solutions by liquid-liquid and liquid-solid extraction.
2. Description of the Prior Art
It is well known in this art, e.g., from Helgorsky et al, U.S. Pat. No. 3,971,843, that gallium can be extracted from basic aqueous solutions, such as sodium aluminate solutions of the Bayer process, by solvent extraction with a substituted 8-hydroxyquinoline dissolved in organic solution. The standard practice for reextracting gallium from an organic solution is to contact the gallium with an aqueous solution of a mineral acid, e.g., hydrochloric, sulfuric or nitric acid. From a process point of view, the acidic re-extraction creates several problems:
a) A high equilibrium acid concentration is required to favorably re-extract gallium from the organic phase, leading either to high acid consumption or to the need for acid recovering stages. PA1 b) The protonation of the substituted 8-hydroxyquinoline when contacted with strong acidic solutions, either increases the acid consumption or requires supplementary acid recovery stages. PA1 c) When gallium is initially extracted from Bayer liquor, any acid mixed with Bayer liquor results in the formation of salts detrimental to the Bayer process, thereby rendering the gallium extraction process less compatible with the host Bayer plant.
It has been suggested in European Patent Application No. 0 234 319, that it may be possible to re-extract gallium from the organic solution by contacting the gallium with a strong base, but no examples are given. Moreover, a concentration of 5 to 10 moles per liter is suggested.
It is an object of the present invention to circumvent the above problems by eliminating the need for acid extraction, thereby rendering the metal recovery process more compatible with the process and solutions used in a hydrometallurgical factory.